Sen. Elizabeth Warren accused Tim Sloan of breaking his promise to customers since he took over as CEO in late 2016 after a fake accounts scandal burst into the headlines.

Last August, Wells admitted it charged nearly 600,000 customers for auto insurance it didn't need. And then it had to admit it improperly charged 110,000 customers fees to extend their mortgage rate locks.

Wells Fargo again finds itself on the hotseat for mistakes it made trying to repay customers hit by improper loan fees.

Sen. Elizabeth Warren, the Massachusetts Democrat who has been highly critical of the bank and its management over numerous issues with customers, fired off a letter to Wells CEO Tim Sloan this week grilling him about botched refunds.

Warren accused Sloan of breaking his promise to customers since he took over as CEO in late 2016 after a fake accounts scandal burst into the headlines. That scandal involved the bank's employees opening accounts without customers' knowledge in a bid to meet aggressive sales goals, an issue affecting millions.

Last August, Wells admitted it charged nearly 600,000 customers for auto insurance they didn't need. And then the bank had to admit it improperly charged 110,000 customers fees to extend their mortgage rate locks.

The Wall Street Journal has reported in recent days that Wells has bungled its reimbursements to the auto loan and mortgage rate lock customers, sending 38,000 incorrect letters to the auto loan customers and forcing mortgage rate lock customers to agree to receive a refund in order to get one.

"Wells Fargo has stolen money from its customers," Warren's letter says. "It has caused thousands of people to spend valuable time and money trying to deal with a problem Wells Fargo created. And now the bank is providing the customers it harmed with inaccurate information or making them jump through hoops just to get their money back."

Her letter seeks answers to several questions by the end of the month, including why it chose to impose an opt-in to get a refund, whether it will admit to revising its refund process and a detailed description of the refund process it intends to use.

A spokeswoman for Wells Fargo issued the following statement in response to questions about the Warren letter:

"Wells Fargo remains focused on making things right for our customers and is working with its regulators to ensure that these ongoing auto and mortgage remediations are completed accurately and as quickly as possible. Our auto remediation is underway and we expect it to be substantially completed by mid-year. We have also begun sending refunds to customers who previously contacted us to question their mortgage rate lock extension fees, and continue to work with our regulators on plans for contacting the remaining customers who paid those fees and invite them to request a refund if they believe that they were charged fees inappropriately. We will address any questions Senator Warren or her colleagues on Capitol Hill have about these plans under way."